On 8 December an attempt was made to destroy Fort Rouge, guarding the entrance to the port of Calais, using one fireship and two catamarans, one of which missed the fort and the other of which failed to explode. This time there were no casualties on either side. A third attack was launched, against Boulogne, on 1 October 1805, but this time employing improved versions of Congreve’s incendiary rockets (which were to produce the ‘rockets’ red glare’ over Baltimore seven years later), and this time the French were taken by surprise and fires started ashore.
Fulton’s fiendish devices were towed into action by Captain Seccombe in a boat rowed by eight men, plus the coxswain, who placed the devices so as to lie on port and starboard sides of a French gun brig anchored in Boulogne Roads. A boat from HMS Immortalité commanded by Lieutenant Payne did the same. On withdrawing, the two officers were disappointed to see that the explosions on each side of their two target vessels appeared to have had no effect. The next morning Fulton was at a loss to explain why the infernal devices had not, as intended, destroyed the French brigs. Later reports in French newspapers confirmed that the explosions had only produced a shock effect and canted the vessels to one side, without damaging them.
Fulton set his analytical mind to work, and realised that if the explosion took place alongside the hull, the blast effect would rise vertically beside the ship. What was needed was a means of ensuring that the explosion took place under the keel. He envisaged the shock wave of a solid body of water being displaced upwards against a small part of the ship’s bottom, which would give way, the explosion having the same effect as if the vessel had been thrown bodily upwards some 20 or 30ft (6 or 9m), and then dropped back down onto a rock 3–4ft (90–120cm) in diameter. He had invented the modern ship-breaking under-keel explosion almost 140 years before it was first used in action.
Nevertheless, he still had to work out how to ensure that his torpedo passed beneath the bottom of the ship to finish up next to the keel instead of merely lying alongside. He kept to his original plan of towing two torpedoes joined together, then releasing them either side of the target vessel’s anchor chain. However, instead of simply attaching the joining rope to the centre of the torpedo tail as at ‘A’ in the above drawing, he arranged the rope so that each torpedo was attached at an angle by a bridle, as in ‘B’ and ‘C’. The action of the tide, represented by the arrow ‘D’, could then be used to swing one or both torpedoes towards the ship and draw it up against the bottom of the hull, where the clockwork fuse would detonate it.
Back in England, to maintain confidence in his towed torpedoes, Fulton put on a demonstration on 15 October 1805 using his new bridle torpedo attachments, in which an old brig, the 200-ton Dorothea, was attacked by rowboats towing two of his modified devices, one of which was filled with 180 pounds (lbs) (82kg) of powder, to be set off by an eighteen-minute delay fuse. After the boats’ crews had practised the operation several times, the real attack went in, and the two torpedoes, joined by 70ft (21.3m) of rope, were released to catch on the Dorothea’s anchor cable. During this manoeuvre one of the observers, Captain Kingston, was heard to declare — presumably on the basis of Fulton’s failure at Boulogne — that if the torpedo were placed under his cabin while he was at dinner, he should feel no concern for the consequences.
Twenty minutes later, just as Fulton had planned, the explosion beneath her keel lifted the brig bodily some 6ft (2m); she broke in half, and both halves rapidly sank. Fulton described the result as ‘in twenty seconds, nothing was to be seen of her except floating fragments’. One is left to imagine that the demonstration drastically changed Captain Kingston’s opinion. The one hundred Royal Navy officers and the government officials present were suitably impressed, but just a week later Napoleon’s hopes of invasion were dashed at Trafalgar. With the threat removed, there was no further employment for Fulton, and he returned home to the States.
On 20 July 1807 he sank a 200-ton brig off Governor’s Island, New York, in front of an audience of some two thousand spectators. He had once more modified the torpedoes, suspending them from floats to keep them several feet below the waterline of the victim. Even so, it took three attempts. On the first, the fuse became inverted, and the priming powder in the flintlock pan fell out, so it did not go off. On the second attempt, the towed torpedoes missed the ship’s cable completely, and blew up 100yds (90m) past her, throwing up an impressive column of water 60 or 70ft (18 to 20m) high. On the third attempt, no doubt to everyone’s delight, the brig was blown up and broke in two, just like the Dorothea.
To make absolutely certain that in future his torpedoes would not miss the target, Fulton proposed a new method of attack. This was described in his treatise on Torpedo War and Submarine Explosions published in New York in 1810 (and from which Fulton’s drawings in this section are taken). He imagined a clinker-built rowboat some 27ft (8.3m) long, with a beam of 6ft (1.8m), single-banked, with six long oars. For self-defence the boat was to be armed with four blunderbusses, mounted one on each quarter (for reasons of clarity they are omitted from the drawing below). Fulton had read a report in a French newspaper of how back in 1805 the blunderbuss in Captain Seccombe’s boat had not only protected them from French musket fire from their intended victim, but had caused the only French casualties in the attack at Boulogne. On the stern of the rowboat was attached a platform, extending out above the rudder and carrying a fifth blunderbuss, but this one was to be loaded with an iron harpoon half an inch (12.7mm) in diameter and 2ft (61cm) long.
A greased rope was attached to the harpoon’s nose, and also to a ring (‘I’ in the drawing above) which, when the harpoon was fired, was free to slide backwards along the shaft, coming to rest in front of a base cup. Fulton designed this arrangement to act as a stabiliser for the harpoon, as a result of up to twenty trial shots, in which he claimed to have never missed a target 6ft square (1.8m × 1.8m) set up at between 30ft and 50ft (9–15m) from the gun. Each time, the head of the harpoon was driven clean through timber 3in (76mm) thick.
On firing the harpoon at an enemy ship’s timber hull, the greased rope would uncoil, and pull the torpedo body after it. The torpedo was to be armed automatically: a separate rope attached to the deck (‘E’ in the drawing of the torpedo boat) would be pulled from the torpedo fuse, setting the clockwork delay mechanism in motion. The torpedo itself was to be suspended beneath the surface from a float cork, and the length of the suspension rope was to be adjusted so as to take into account the draught of the vessel being attacked, to ensure the torpedo finished up underneath the keel. Fulton had invented a simple torpedo depth setting.